Thymosin .alpha..sub.1 occurs naturally and its isolation and biological activity has been described in U.S. Pat. No. 4,079,127. Thymosin .alpha..sub.1 is a biologically active peptide hormone isolated from thymosin fraction 5 and has its amino-terminus acetylated. The preparation of desacetyl thymosin .alpha..sub.1 by solid state synthesis is described by Wong and Merrifield, Biochemistry 19, 3233-3239 (1980), and, therefore, is available as a starting material in producing thymosin .alpha..sub.1.
In U.S. patent application Ser. No. 137,939, filed Apr. 7, 1980, now U.S. Pat. No. 4,293,455 for N.sup..alpha. -DESACETYL THYMOSIN .alpha..sub.1 AND PROCESS [inventors: Merrifield and Wong], there is disclosed the conversion of [Lys (Tfa).sup.14,17,19,20 ]-desacetyl thymosin .alpha..sub.1, produced by solid state synthesis, into thymosin .alpha..sub.1 by acetylation with pyridine-acetic anhydride, followed by removal of the trifluroacetate (Tfa) protecting group with aqueous pyridine.
Bloemendal, H. Science 197, 127-138 (1977) has reported that both enzymes and structural proteins may be acetylated by other proteins at the amino-terminus, with acetylation taking place on the nascent protein chain containing 25 or more amino acid residues during biosynthesis of the chain [Palmiter, R.D., et al., Proc. Nat. Acad Sci 75 9498 (1978)]. An enzyme present in extracts from calf lens will acetylate synthetic desacetyl .alpha.-melanocyte stimulating hormone [Granger, et al. Proc. Nat. Acad. Sci 73, 3010-3014 (1976)]. A pituitary enzyme preparation will transfer acetyl groups from acetyl-Coenzyme A to ACTH and ACTH fragments [Woodford and Dixon, J. Biol. Chem. 254, 4993-4999 (1979)]